A conventional door-closer as shown in FIGS. 9 and 10 operates on the principle of a shock absorber in which a piston P moves in a cylinder for forcing oil through small openings respectively provided in the piston and cylinder. When the door is opened, the piston is withdrawn and the oil in the cylinder opens a ball valve in a passage provided in the piston and flows into the space to the right of the piston (FIG. 9). When the door is released, it is closed by the action of the spring and the piston travels back to the right and forces the oil through the return passages (FIG. 10) into the space to the left of the piston to gradually slow down the closing of the door because the oil escape is progressively cut off by the advance of the piston.
However, such a conventional door-closer still has the following defects:
1. The piston P is reciprocatively moved within the cylinder as actuated by a spindle S and a link means M to form a gigantic structure and complex mechanism to thereby increase the production cost, installation space and maintenance problems.
2. The door can only be opened or closed in a single direction to limit its application, for instance, in a two-way (in-and-out) door system.
3. The force to open a door is not always normal to the force arm (not forming 90.degree.) to thus consume much energy and to easily cause tiredness for a door opener.
The present inventor has found the defects of a conventional door-closer and invented the present door-closer hinge with rotary-movement shock absorber.